The ADC field includes a variety of different types of ADC data carriers and ADC readers operable to read data encoded in such data carriers. For example, data may be encoded in machine-readable symbols, such as barcode symbols, area or matrix code symbols, and/or stack code symbols. Machine-readable symbols readers may employ a scanner and/or imager to capture the data encoded in the optical pattern of such machine-readable symbols. Other types of data carriers and associated readers exist, for example magnetic stripes, optical memory tags, and touch memories.
Other types of ADC carriers include RFID tags that may store data in a wirelessly accessible memory, and may include a discrete power source (i.e., an active RFID tag), or may rely on power derived from an interrogation signal (i.e., a passive RFID tag). RFID readers typically emit a radio frequency (RF) interrogation signal that causes the RFID tag to respond with a return RF signal encoding the data stored in the memory.
Identification of an RFID tag generally depends on RF energy produced by a reader or interrogator arriving at the RFID tag and returning to the reader. Multiple protocols exist for use with RFID tags. These protocols may specify, among other things, particular frequency ranges, frequency channels, modulation schemes, security schemes, and data formats.
Many ADC systems that use RFID tags employ an RFID reader in communication with one or more host computing systems that act as central depositories to store and/or process and/or share data collected by the RFID reader. In many applications, wireless communications is provided between the RFID reader and the host computing system. Wireless communications allow the RFID reader to be mobile, may lower the cost associated with installation of an ADC system, and permit flexibility in reorganizing a facility, for example a warehouse.
RFID tags typically include a semiconductor device having the memory, circuitry, and one or more conductive traces that form an antenna. Typically, RFID tags act as transponders, providing information stored in the memory in response to the RF interrogation signal received at the antenna from the reader or other interrogator. Some RFID tags include security measures, such as passwords and/or encryption. Many RFID tags also permit information to be written or stored in the memory via an RF signal.
RFID tags are generally used to provide information about the specific objects on which the RFID tags are attached. For example, RFID tags may store data that provide the identification and description of products and goods, the identity of an animal or an individual, or other information pertaining to the objects on which the RFID tags are attached.
Some types of RFID tags are capable of communicating with each other, thereby allowing formation of an RFID network. However, direct tag-to-tag communication in such RFID networks is currently possible only between specially designed battery-powered active RFID tags, such as the products available from Axcess Inc. and/or the devices used in the “Smart Dust: Autonomous sensing and communication in a cubic millimeter” project described in http://robotics.eecs.berkeley.edu/˜pister/SmartDust/. Such active RFID tags and devices can be unduly complex in design and expensive, especially in situations requiring a large number of tags where the batteries have to be continuously monitored, maintained, and replaced in order to ensure that sufficient power is available to meet operational requirements.
Moreover, traditional client-server applications and methods are not particularly suited for RFID networks that need to be capable of handling very large numbers of interconnected RFID tags in an ad hoc manner. In addition, the RFID tags may dynamically join or leave the RFID network due to a number of reasons, such as exhaustion or lost of power, signal attenuation, physical destruction, etc. The dynamic and generally random nature of the interconnection between and presence of RFID tags, combined with a potentially massive number of distributed RFID tags, as a practical matter preclude the use of traditional applications and methods for communications.
As an additional consideration, the routing table approach used in wired networks and in wireless networks (such as 802.11, ZigBee, Bluetooth, etc. wireless systems) requires a relatively large amount of memory, which is not readily available in RFID tags and therefore cannot be conveniently used in RFID networks. Furthermore, the traditional communication applications and methods are generally unsuitable in RFID networks where the complexity of interconnections between RFID tags requires such communication applications/methods to address scalability, pervasiveness, spatial distribution, power awareness, and/or other issues.